Category 1, 2 and 3 water — and why the answer changes while you're standing there

Every water job starts with one call, and everything else follows from it. How dirty is this water?

Get it right and the rest of the job makes sense. Get it wrong and you've picked the wrong PPE, left material in the building that should have gone, and told a family it was safe to sleep in a house where it wasn't.

Most explanations of this stop at the definitions. The definitions are the easy part.

The three categories

Category 1 is clean water. It's come from a sanitary source and carries minimal risk from skin contact, swallowing it or breathing near it. A burst supply line. Rainwater through a roof. A toilet cistern with nothing added to it.

Category 2 is grey water. Enough contamination that it can make someone sick if they swallow it or it gets into a cut. Unsafe levels of microorganisms or chemicals. Dishwasher and washing machine discharge. A toilet overflow with urine but no solids. A punctured waterbed.

Category 3 is black water. Grossly contaminated — harmful pathogens, toxins or chemicals, and a high risk of harm through any kind of contact. Sewage. Floodwater. A creek or river that's come up. Wind-driven rain. It can also carry regulated material like lead, asbestos or fuel.

Fine. Now the part that matters.

Category is not a fixed property of the water

It's a description of two things: where the water came from, and what it's been in contact with since.

That second half is what people miss. Clean water that's run through a filthy subfloor isn't clean any more. It hasn't changed source. It's changed category.

And it keeps changing. Time and temperature drive contaminant growth. Microorganisms already sitting on the materials in a building wake up when they get wet and start multiplying, and how fast depends on how long they stay wet and how warm it is. A Category 1 loss left over a hot Brisbane weekend is not a Category 1 loss on Monday.

There's a useful rule of thumb in the distinction between two situations. Clean water into an uncontaminated building won't change category quickly. Clean water into a contaminated area can change category immediately.

Immediately. Not after 24 hours, not after 72. The moment it flows into somewhere already dirty.

What that means when you turn up

Ask when the water started, not when the call came in. Those are often days apart, and the clock that matters started at the first one.

Use your nose. A degrading Category 1 will often tell you before any meter does — that's what the odour is.

And be honest in the assessment rather than optimistic. Calling something Category 1 because the paperwork is simpler is how people end up drying a contaminated building.

What has to come out

Once it's Category 2 or worse, the sequence changes. You remediate first, then dry. Drying a contaminated building spreads the contamination around and bakes it in.

Category 2 and 3 both require removal of carpet padding, HVAC insulation, particleboard, multi-layer flooring and wall insulation.

Category 3 adds drywall, ceiling tiles, wallpaper, soundboard, carpet and cushion.

Alongside that: find and stop the contamination source, contain the area with barriers and negative pressure, clean your equipment between areas so you're not carrying it room to room, and use HEPA vacuums and inline filters. A standard vacuum puts the contaminants you're removing straight back into the air.

Full PPE, not partial. Gloves, goggles, boots and respiratory protection matched to what you're actually in.

When to bring someone else in

Some jobs shouldn't be called by the tech on site alone. An independent indoor environmental professional gets involved when there are high-risk occupants — elderly, children, immunocompromised — or in public health settings like hospitals, childcare and aged care. They confirm the category and handle clearance testing.

That's not a lack of confidence. It's the right call, and knowing when to make it is part of the job.

Write down why, not just what

"Cat 2" is not documentation. It's a label.

This is documentation: Cat 2 — washing machine discharge, standing approximately 36 hours per occupant, no solids present, odour detectable in hallway.

The difference matters months later when someone asks why you removed a floor. The first version gives you nothing to stand on. The second explains itself.

Every downstream decision on the job — PPE, removal, remediation before drying, equipment, what the insurer pays — hangs off this one call. It's worth the extra two minutes.